We report the results of an experiment where after 30 test trials the mean value of known external friction impulses acting on a three-body system accounted for only ~ 8.2 per cent (standard deviation .037 and standard error .0068) of the increase in the final momentum of the system, leaving a ~ 91.8 per cent discrepancy due to an unknown impulse. In this paper we propose an explanation for this impulse that accounts for this discrepancy. The three-body system consisted of two spheres, constrained to roll around quarter-circle barriers attached to a third body. As the spheres rounded the curves, centripetal contact forces acted on the spheres while equal and opposite centrifugal reactive contact forces acted on the inner walls of the curved barriers. These centrifugal reactive contact forces caused the system to accelerate, inducing fictitious body forces on the spheres that increased their orbital angular speed. We cite Einstein’s principle of equivalence to explain this increase in speed.